Equipment for controlling and monitoring the electron beam of a horizontaltype particle accelerator



D 12. 1 67 s. FRANKE ETAL.

EQUIPMENT FOR CONTROLLING AND MONITORING THE ELECTRON BEAM OF amid; N

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EEFQME wuzwmwlwm mmIFuwm mxOIo ow w wzjmnouwa A HORIZONTAL-TYPE PARTICLEACCELERATOR Filed. July '27, 1965 IN VENTORS SIEGFRIED FRANKE SIEGFRIEDGROSSE BERND-DIETRICH TORGE AGENT Dec. 12, 1967 v EQUIPMENT FORCONTROLLING AND MONITORING THE ELECTRON BEAM OF A HORIZONTAL-TYPEPARTICLE ACCELERATOR 2 Sheets-Sheet 2 Filed July 27, 1965 FIG. 2

S. FRANKE ETAL AGENT United States Patent EQUIPMENT FOR CONTROLLING ANDMONITOR- IN G THE ELECTRON BEAM OF A HORIZONTAL- TYPE PARTICLEACCELERATOR Siegfried Franke, Siegfried Grosse, and Bernd-DietrichTorge, Dresden, Germany, assignors to VEB Transformatorenund RontgenwerkDresden, Dresden, German y Filed July 27, 1965, Ser. No. 475,176

Claims. (Cl. 328233) ABSTRACT OF THE DISCLOSURE Equipment forcontrolling and monitoring the electron beam of a horizontal particleaccelerator, with electromagnet means at the outlet end of theaccelerator tube, having two windings, of which one is excited by directcurrent and serves to deflect the beam from horizontal into vertical,while the other is excited by a low-frequency alternating current forfanning out the deflected electron beam.

The present invention relates to an equipment for controlling andmonitoring the electron beam of a horizontaltype particle accelerator,where an electromagnet is provided at the outlet or exit end of theaccelerator tube, whose one winding is excited by a direct current andwhich thus serves to deflect the electron beam from the horizontal intothe vertical, while the other winding of the magnet is excited by alow-frequency, sinusoidal, triangular or saw-tooth-shaped current andwhich thus serves to fan out the deflected electron beam. In a preferredembodiment, two coil structures may be provided, With serially connectedwinding portions.

The application of high-speed electrons in radiation chemistry and forsterilizing foods, medicines, surgical dressings and medical instrumentsrequires, in addition to a powerful generator for the production andacceleration of the electrons, the so-calied particle accelerator, anadditional equipment which feeds the electron beam, which is focusedafter passing through the accelerator tube of the particle accelerator,to the material to be irradiated with uniform intensity and possiblywithout any loss of energy.

The material or object to be treated is usually passed under thevertically arranged arrangement which also includes the aforementionedadditional equipment. The latter consiss of an electromagnet at the exitend of the accelerator tube, excited by a low-frequency sinusoidal,triangular or saw-tooth-shaped current and performing the fanning out ofthe focused beam to a variable degree, depending upon the amplitude ofthe exciting current.

The material passes, as a rule, on a conveyer belt under the exit windowof the particle accelerator. Due to the fanning of the electron beam,arriving perpendicularly from above in vertical-type particleaccelerators, the beam can be adapted to the width of the material to beirradiated so that a uniform distribution of the beam dose on thesurface of the irradiated material is achieved, and on the other hand,the beam exit window of the particle accelerator, which usually consistsof a very thin aluminum foil, is under a uniform thermal stress.

In vertical-type particle accelerators it is known manually to adjustthe amplitude of the sinusoidal, triangular or saw-tooth-shaped currenteffecting the fanning out of the electron beam, thus adapting it to theWidth of the particular material to be irradiated. The extent of thefanning is measured and controlled by either differentiating thesinusoidal, triangular or saw-tooth-shaped impulses at the exciting coilof the electromagnet, after which they Patented Dec. 12, 1967 arerectified and indicated on an ammeter, or by making the differentiatedimpulses at the exciting coil of the electromagnet visible on the screenof an oscilloscope.

Such a measurement and control of the fanning width of the electron beamis very inaccurate, since even minor variations of the accelerationvoltage, which cannot always be sensed, can vary the fanning widthwithout this being recognized from the indicated electric values derivedfrom the exciting current of the electromagnet. Furthermore, the use ofa vertical-type particle accelerator is in many cases not feasibleinsofar as it has a relatively great overall height, due to the highacceleration voltages, and therefore cannot be always installed withoutadditional constructional expenditure. Besides, the disassembly of thehigh-voltage generator and/or particle accelerator in case of aninspection is difiicult in the vertical arrangement.

These last-mentioned disadvantages of the vertical-type arrangement arenot found in a horizontal-type particle accelerator since the highacceleration voltages have only a minor eifect on the overall height andrather affect the overall length of the entire set-up. Such particleaccelerators can, therefore, be used practically everywhere withoutadditional constructional expenditure, apart from the necessaryradiation protection. The disassembly in case of an inspection is simplesince the pressure tank, for example, surrounding such a particleaccelerator equipment can be removed from the active portions of theequipment after loosening a few connections.

But in addition to fanning out the electron beam, it is necessary in ahorizontal-type particle accelerator to deflect the electron beam fromthe horizontal into the ver tical, that is, by an angle of degrees, ifthe material to be irradiated is to pass on a conveyer belt under thebeam exit window.

This is achieved by providing the electromagnet arranged at the outletend of the acceleration tube with a winding for fanning out the electronbeam, excited by a sinusoidal, triangular or saw-tooth-shaped current,and with an additional winding which is excited by a direct current andwhose magnetic field effects the 90 deg. deflection of the electronbeam. The windings may be combined into one or two adjacent coilstructures.

In addition to the above-mentioned difficulty of measuring exactly, andrespectively controlling the size of the electron-beam fanning effect,and taking into account any variation of the acceleration voltage thatcannot be ascertained and therefore not corrected, there is here anadditional difiicuity, namely of keeping the deflection of the electronbeam constant at an angle of 90 degrees, independent of theabove-mentioned, not always determinable variations of the accelerationvoltage, and of precisely adapting it to a deliberate variation of thelatter.

If the deflection of the electron beam difiers from 90 deg. due to awrong adjustment of the direct current exciting the electroinagnet ordue to an undetei'minable variation of the acceleration voltage, theelectron beam could run under certain circumstances against or impingeupon the walls of the deflection chamber or the tube, and the X-raysthus produced, which are very hard owing to the very high accelerationvoltages, can cause considerable secondary damages.

One of the main objects of the invention is to eliminate thedisadvantages and difficulties encountered in the control of thedeflected and fanned-out electron beam of known particle accelerators.

It is one object of the invention to provide an equipment forcontrolling and monitoring the electron beam of a horizontal-typeparticle accelerator, which permits, on the one hand, an accurateadjustment of the direct current deflecting the electron beam from thehorizontal into the vertical in dependence on the prevailing, adjustedacceleration voltage, and on the other hand, an automatic correction ofdeviations in the deflection angle due to unavoidable differences of theacceleration volt age.

Another object is to permit the adaptation of the electron-fan width tothe actual width of the irradiated material, possibly automatically, andthe indication or automatic correction of the variations in the width ofthe electron-beam fan caused by operational factors, for example,undeterminable variations of the acceleration voltage, so that anoptimum distribution of the radiation dose on the irradiated material isachieved.

This problem is solved, according to one of the important features ofthe present invention, by providing a generator supplying the directcurrent for the deflection of the electron beam with a preferablyelectronic adjusting element which is, on the one hand, controllable byan electric parameter proportional to the acceleration voltage of theparticle accelerator, preferably by the column current of thehigh-voltage generator, and is, on the other hand, regulable independence on the size of the output voltages of a probe assemblyarranged in front of the beam exit window of the particle acceleratorand adjustable according to the prevailing irradiating conditions.

Another feature relates to making the generator which supplies thelow-frequency, sinusoidal, triangular or sawtooth-shaped current forfanning the electron beam, regulable over an additional, preferablyelectronic adjusting element in dependence on the size of the outputvoltages of the probe assembly.

An advantageous and preferred embodiment of the equipment according tothe invention comprises two probes which can be set oppositely andsymmetrically to the central beam, corresponding to the width of thematerial to be irradiated, and which are so arranged in front of thebeam exit window of the particle accelerator that they are onlyirradiated partly, preferably half, with the correct size and positionof the fanned-out electron beam, corresponding to the setting of theprobes and thus to the width of the material to be irradiated; theprobes attain in this case the nominal value of their output voltages.

The two probes are so connected electrically, over a rectifier and/or asmoothing element, with two variablegain amplifiers acting asdifferential amplifiers that the sum of the rectified and/or smoothedoutput voltages of both probes is in one amplifier oppositely connectedto the constant voltage of a reference voltage source, and that theamplified difference of these voltages, in case it differs from apre-determined nominal value, influences the adjusting element of thegenerator supplying the sinusoidal, triangular or saw-tooth-shapedcurrent for fanning out the electron beam, so as to increase or decreasethe amplitude of this current.

In the second variable amplifier acting as a differential amplifier therectified and/ or smoothed output voltage of one probe is oppositelyconnected to that of the other probe, and the amplified difference ofthe voltages, in case it likewise differs from a pre-determined nominalvalue, influences, together with the electric parameter proportional tothat of the acceleration voltage of the particle accelerator, theadjusting element of the generator supplying the direct current fordeflecting the electron beam, so as to increase or decrease the lattercurrenb.

It seems particularly advantageous, according to an inventive concept,if the nominal values of the rectified and/or smoothed output voltagesare equal and if their sum corresponds to the size or level of theconstant voltage of the reference voltage source. With such an arrangement of the probes, the voltage at the output of the twovariable-gain amplifiers is zero when the probes attain their nominalvoltage values, that is, when they both are, for example, halfirradiated, so that the size and position of the fanned-out electronbeam corresponds to the setting of the probes and also to the width ofthe irradiated material.

The adjusting elements for the two generators must have in this caseeither a high zero-point sensitivity or the outputs of the variableamplifiers must be superposed on a constant voltage at the inputs of theadjusting elements.

Another feature suggested by the invention provides a series arrangementof two pairs of probes which can be set oppositely and symmetrically tothe central beam, corresponding to the width of the material to beirradiated, in front of the exit window of the particle accelerator inthe fanning direction of the electron beam, in such a way that theindividual probes of each pair which are closest to the central beam arecompletely irradiated with the correct size and position of thefannedout electron beam, corresponding to the setting of the probes,while the probes of each pair arranged on the outside in fanningdirection are only partly irradiated, and all probes attain in this casethe nominal values of their output voltages. The pair of probes closestto the central beam and that arranged on the outside in fanningdirection are each electrically connected with an amplifier which makesthe irradiation of the respective probes visible, for example, overmagic fans or electronbeam indicators.

The probes closest to the central beam are preferably also electricallyconnected with a variable-gain amplifier acting as a differentialamplifier by way of a rectifier and/ or a smoothing element. Therectified and/ or smoothed output voltage of one probe is oppositelyconnected in this amplifier to the output voltage of the other probe, asalready described in the first embodiment of the equipment, and theamplified difference of these voltages influences, here again, togetherwit-h the electric quantity proportional to that of the accelerationvoltage of the particle accelerator, the adjusting element of thegenerator supplying the direct current for deflecting the electron beam,so as to increase or decrease this current, in case said voltagedifference deviates from a pre-determined nominal value.

The amplitude adjustment and correction of the sinusoidal, triangular orsaw-tooth-shaped current for fanning out the electron beam is noteffected here over a closed electric control circuit and an electronicadjusting element, but by hand, on the basis of the optical indicationby the electric eyes over a manual adjusting element, the circuit beingthus closed or completed by the operato-r.

This embodiment of the invention seems of advantage wherever, due tosubstantially constant irradiation conditions, an automatic setting andcorrection of the electronbeam width is not imperative or where, due tothe size and the utilization of the irradiation equipment, such anautomatic setting and/or correction would not be economicallyjustifiable.

In order to prevent the secondary electrons issuing from the irradiatedmaterial and the electric charges applied to the irradiated material bythe electron beam, in case of an electric insulating material, frominfluencing the probes arranged in front of the beam exit window of theparticle accerelator and from falsifying their output voltages, it isadvisable, according to yet another inventive feature, to arrangegrounded metal diaphragms between the probes and the irradiatedmaterial, adjustable together with the probes, in such a way that theyonly cover the surface of the respective probes toward the ma terial tobe irradiated.

According to a further feature, relating to an improvement of theequipment according to the invention, the

generator supplying the current for the deflection of the electron beamproduces a sinusoidal current, for example, distorted by non-linearcircuit elements. It was found that if the electromagnet is excited, forexample, with such J sinusoidal current distorted by magnetization, theelectron beam is so conducted over the irradiated material that anoptimum distribution of the radiation dose over the material isobtained.

The preferred embodiment to be described hereinafter has the advantagethat the direct current for the deflection of the electron beam adjustsitself automatically depending on the selected acceleration voltage sothat misadjustments and the resulting secondary damages are avoided.

The adjustment of the probe assembly in front of the beam exit window ofthe particle accelerator permits furthermore a simple adjustment of theelectron-beam fan width to the width of the irradiated material and asimple indication, control and correction of its location and width.

Due to the action of the regulating circuit for the deflection and thefanning out of the electron beam, the particle accelerator is completelyreliable even over prolonged periods, and additional measures forkeeping constant the currents for the deflection and the fanning out ofthe electron beam, and for the acceleration voltage, are unnecessary andcan be dispensed with.

The various objects, features and attendant advantages of the presentinvention will become more apparent from the following description oftwo preferred embodiments of the electron-beam controlling andmonitoring equipment according to the invention, when considered inconjunction with the accompanying drawings, wherein FIG. 1 shows theelectric block circuit diagram of a first embodiment of the inventiveequipment, with some of the structural elements of the generator,accelerator tube, irradiation system, probes, conveyer with material tobe irradiated, also shown structurally, and having a closed electricadjusting circuit each for the deflecting and the fanning-out of theelectron beam; and

FIG. 2 is a similar circuit diagram, with some structural elementsbroken away, of a second embodiment of the equipment, having a closedelectric adjusting circuit for the electron-beam deflecting circuit, andanother adjusting circuit to be operated by the attendant of theirradiating equipment, for the electron-beam fanning-out circuit, withvisual indicating means.

FIG. 1 illustrates a high-voltage generator generally designated 2 (someof the inner parts being shown in phantom); preferably, aVan-De-Graatf-type generator is employed. The generator is connected toan accelerator tube 4 of the particle accelerator. A mains supply unit 6feeds the generator 2 with the necessary D-C high voltage, e.g. from anAC mains, as indicated. The intercalated, relay-operated contacts willbe described somewhat later.

At the outlet end of the accelerator tube 4 is arranged an irradiatingunit generally denoted 8 which incorporates an electromagnet 10 ofwhich, schematically, two windings are shown. One winding serves todeflect the electron beam by 90 degrees (horizontal path withinaccelerator tube 4 and vertical path in unit 8), while the otherperforms the fanning out of the deflected beam, in a direction at rightangles to the advance movement of the materials, as shown inside theunit 8. The horizontal electron beam inside the tube 4 is identified bynumeral 80, while the fanned-out, plural, downwardly directed beamportions are identified by 82. In connection with the two windings ofthe electromagnet 10, it should be noted that for practical purposes, ithas been found advantageous to provide two coil structures incorporatingtwo Winding portions each, serially connected in the deflecting andfanning feed paths. This has been shown schematically in FIG. 1 wherein,however, single leads have been shown and thus the return leads areomitted in both paths.

The windings or winding portions of electromagnet 10 are respectivelyconnected to an A-C generator and to a D-C generator which perform thefanning out and the deflection of the electron beam 80; theinterconnecting electric feed lines have only schematically beenindicated.

6 The generators will be fully described as the specification proceedswith the description of the electric circuit.

The beam 82 is guided within a structure schematically shown at 12 andhaving a bottom exit window 14 in a bottom plate 12', preferably madefrom copper and having water cooling (not illustrated for the sake ofclarity).

A conveyer belt system schematically shown at carries materials orobjects shown by a block 92, which are to be irradiated. For example,foods, medicines, surgical dressings and medical instruments may besubjected to the irradiation by the equipment according to the presentinvention. The electron beam 82 strikes the materials or objects 92which are moved in a direction substantially perpendicular to thefanning of the beam, along the elongated exit window 14.

Between the window 14 and the material 92 to be irradiated are arrangedtwo probes 16a, 16b, preferably made from tungsten, which are slidablymounted so that they can be adjusted by hand according to the width ofthe material 92 and at the same time symmetrically to the centralelectron beam, as shown by the double arrows thereunder. The probes 16a,16b are highly insulated and electrically shielded from the rest of thestructure 12. The adjusting means are not illustrated.

The arrangement of the probes 16a, 16b is such that they are onlyirradiated half, with correct positioning and width of the electron beam82 with respect to the Width of the irradiated material 92, and thatthey attain in this arrangement the nominal value of their outputvoltage impulse. Between the probes 16a, 16b and the material 92 arearranged grounded metal diaphragms 18a, 18b which can be adjustedtogether with the probes. These diaphragms cover only the surfaces ofthe probes 16a, 16b, respectively, facing the irradiated material 92 andkeep off secondary electrons issuing from the material, while theyground the electric charge applied to the material 92 if this iselectrically insulating. In the latter case, the material wouldaccumulate an electric charge which unfavorably influences the probes.

The pulses derived from the probes 16a, 1622 are fed to respectiveamplifiers and smoothing elements 29a, 20b, as shown in the blockdiagram of FIG 1, where these output pulses are rectified and/ orsmoothed. The D-C voltages thus obtained are conducted both to theinputs of first and second variable-gain amplifiers 22 and 24.

In the amplifier 22, the sum of the voltages arriving from the units 20aand 20b is oppositely connected to a constant voltage supplied by areference voltage source 26. It should be noted that, for the sake ofclarity, conventional mains and other supply leads have been omitted,from unit 26 as well as from the others shown in the circuit diagram.

The sum of the nominal values of the rectified and/or smoothed outputvoltages of probes 16a, 16b corresponds to the magnitude of the voltageof the source 26 so that, in case both probes are irradiated half by thefannedout electron beam 82, the difference between the sum of thevoltages arriving from the units 2641 and 20b and the voltage derivedfrom unit 26 is zero. There is consequently no control or adjustingorder at the output of the variable amplifier 22, acting as adifferential amplifier, in the direction of the A-C generator to bedescribed shortly.

If the probes 16a,

16b are not irradiated at all, or less than half, due to aninsufliciently fanned-out beam 82, the sum of the output voltages of theprobes is zero or, respectively, below the nominal value. Thus at theoutput of the amplifier 22 there appears the full amplified voltage ofthe reference voltage source 26 and the amplified difference,respectively, with a positive sign, for example, as a control oradjusting order.

At 28 an A-C generator is schematically shown which produces a distortedsinusoidal current for fanning out the electron beam 80, by way of oneof the windings of I magnet 10, as has been described before. Thegenerator 28'has an electronic adjusting circuit or element 282, e.g. inthe form of an electron-tube circuit in, or acting on, the final stageof the generator 28. The control or adjusting order derived fromamplifier 22 is fed to the adjusting element 282 which in turn increasesthe amplitude of the sinusoidal current until, on effect of the changesin the electromagnet 10 of the irradiating unit 8, the beam 82 ischanged in its width and the probes 16a, 16b are half irradiated; now,again, the difference of the voltages at the input of the amplifier 22becomes Zero.

The same process takes place, but with an opposite sign, when the probes16a, 16b are completely irradiated or more than half. The sum of therectified and/ or smoothed voltages of the probes is then greater thanthe voltage from the source 26. At the output of the amplifier 22 theamplified difference appears with a negative sign, so that the adjustingelement 282 reduces the amplitude of the sinusoidal current supplied bythe generator 28 to the unit 8, until the probes 16a, 16b are again halfirradiated.

The foregoing considerations apply to all cases where the fanned-outelectron beam 82 is symmetrical to the central beam and the deflectionis therefore correctly 90 degrees, but is fanned out too little or toomuch for the actual spatial setting of the probes 16a, 16b, and for thewidth of the irradiated material 92, respectively.

Before describing the role of the second variable-gain amplifier 24, thesource of direct current will be explained, which performs thedeflection of the beam 80, by Way of the other winding of the magnet 10,as has been described before. At 30 a DC generator is schematicallyshown for this purpose; a decoupling choke 32 is seriesconnected betweenthe generator and the appropriate winding of the electromagnet 10, and abranch line is shown between the output side of the choke 32 and thesecond amplifier 24.

The value of the D-C current output of generator 30 depends on theenergy which the electrons receive on their path through the acceleratortube 4; in other words, on the acceleration voltage of the particleaccelerator. A voltage divider is constituted by resistors 342 and 344,the former being within the high-voltage generator 2 while the latter,grounded at its free end, is preferably arranged outside. The columncurrent flowing through the voltage divider, generally identified as 34,is directly proportional to the acceleration voltage.

The column current flowing through the voltage divider 34 should befurther explained by stating that the highvoltage source 6 supplies D-Cof approx. 60 kv. to concentric, vertical ring members disposed withinthe generator 2 (preferably of the known Van de Graaif type), as shown;in FIG. 1, the extreme left-hand ring member is connected to the freeend of the resistor 342; this, in turn, is connected to the end resistor344. The negative terminal or the D-C high-voltage supply unit 6 as wellas the other end of resistor 344 are both grounded, closing thereby thecircuit. The accelerating voltages produced by the high-voltagegenerator 2 are in the range of l to MV. The afore-mentioned ringmembers are the highvoltage electrodes of the generator 2.

The resistor 344 has a tapping for deriving thereat a voltage producedowing to the voltage drop over this part of the voltage divider 34, dueto the column current; this voltage is fed to an electronic adjustingelement 302 associated with the generator 30. Unit 302 may, again, be aconventional electronic control circuit. It automatically adjusts thevalue or magnitude of the deflecting direct current depending upon theacceleration voltage.

As has been explained somewhat earlier, the D-C outputs of the units20a, 28b are also fed to the second amplifier 24. Here the inputs areoppositely connected. If the deflection of the electron beam 82 deviatesfrom 90 degrees, e.g. due to fluctuations of the acceleration voltagewhich cannot always be avoided, either the probe 16a or the probe 16b isirradiated more while the other is irradiated less, or vice versa,regardless of possibly proper fanning width.

In either case we obtain at the input of the amplifier 24 a voltagedifference with either a positive or a negative sign, which appearsamplified at the output of this amplifier 24, and which serves as acontrol or adjusting order for the afore-mentioned adjusting element 302of the D-C generator 30. The unit 302 either increases or decreases thedirect current of the generator 30, fed to one of the windings ofelectromagnet 10, until both probes 16a,-16b are again uniformly andequally irradiated, that is, until the voltage difference atthe input ofthe variablegain amplifier 24 is zero again.

In order to prevent the two above-described control circuits frominfluencing each other if an unsymmetry and at variation of the width ofthe fanned-out electron beam should appear simultaneously, thus causinginstabilities and adjusting variations, e.g. in the units 282 and/ or302, the time constants of the two control circuits are made to havedifferent values. Appropriate means (not further described) may beincorporated either in one or both of the amplifiers 22, 24, or in oneor both of the units 282, 382.

In addition, in order to insure the stability of the control circuit forthe electron-beam deflection, acting by Way of the D-C generator 30, anelectric feed-back circuit 36 is provided from the output of thegenerator 30 (after the choke 32) to the input of the amplifier 24; thisis the branch line which has already been mentioned when describing thegenerator 30 and the choke 32.

Both the AC generator 28 and the D-C generator 30 act on a protectivecircuit designated 38 which shuts off the particle accelerator, that is,the acceleration voltage, should one of the generators 28, 30 fail.Although input leads are shown to circuit 38 from both generators 28 and30, only the former is shown in some detail. A thyratron 382 is shownwith an appropriate network 384 including separating, voltage droppingand other electronic elements known per se. The circuit in unit 38associated with the generator 30 is similar to that shown and operatesin parallel so that failure of either generator has the same effect.

The plate current of thyratron 382 may feed, for example, a relay 40which is connected to the common mains input. The singleor double-polecontact of this relay will interrupt the mains-input circuit of the DCsupply 6. It will be understood that the protective circuit 38, as wellas the relay 40, may be of the normally energized or normallydeenergized type, depending upon local operational requirements.

In the protective circuit described for FIG. 1, the thyratron may,preferably, be made open or conductive when the deflection voltage forthe electron beam is present; the thyratron closes if the deflectionsystem fails, opening thereby the relay circuit, and interrupting themainsor D-C high-voltage supply.

It should be noted that the circuit 38 may be separate from or combinedwith the mains-supply unit and/or the necessary high-voltage source,like shown at 6. Such a modification will be explained in connectionwith the second embodiment shown in FIG. 2, to be described hereafter.

FIG. 2 illustrates a second preferred embodiment of the inventiveequipment, wherein identical or basically similar elements have beendesignated with the same reference numerals. Part of theirradiating-unit structure has been omitted. In addition to the alreadydescribed probes 16a, 16b, this modification also comprises a sec- 0ndpair of probes 46a, 46b, arranged side-by-side with the afore-mentionedprobes. The probes 46a, 46b are arranged symmetrically with respect tothe central beam and w more outwardly than the probes 16a, 16b. They aremanually adjustable, again as shown by double arrows.

At least the outer probes 46a, 46b can be adjusted with respect to theelectron beam and/or to the other elec- 9 trodes 16a, 16b. The adjustingstructure is generally designated 48 and may include, for example, atransversal rail member with appropriate tightening means (e.g. clampsand screws), preferably on both sides of the guide structure 12 (onlythe adjusting means behind it being shown).

The arrangement is such that while the probes 16a, 16b (closer to thecentral beam) are completely irradiated with thefanned-out beam (like 82in FIG. 1), in case of its being properly positioned as to symmetry andwidth, in accordance with the irradiated material 92, the probes 46a,46b are only partly irradiated. All four probes, however, attain thenominal value of the output impulses.

The output pulses of the probes 16a, 16a are fed into a first indicatingamplifier 42, and the pulses of the probes 46a, 46b into a secondindicating amplifier 44; both amplifiers have combined so-called magiceyes or electronbeam indicators 422, 442, respectively, each forsimultaneous indication of two parameters, for comparison purposes. Onthe basis of the optical indications given at 422, 442, the operator canreadily check the agreement of the width of the fanned-out electron beamby monitoring the indicator 422 (via probes 16a, 16b) and the indicator442 (via probes 46a, 46b), respectively, comparing it with the width ofthe irradiated material 92. If necessary, manual corrections can be madeby way of a control knob,286 operating an electronic adjusting element284 of the A-C generator 28. This will regulate the fanning-out of theelectron beam 82 to the width of the material 92.

It will be understood that the adjusting element 282 of generator 28(FIG. 1) provides automatic regulation of the variable output, while theadjusting element 284 shown for the same generator in FIG. 2 representsa potentiometer or other manually adjustable control element, having acontrol knob 286 or like manual means of adjustment.

In addition to the amplifiers 42, 44, the output voltage pulses of theprobes 16a, --16b are, here again, fed together to a rectifier and/ orsmoothing element 20 (instead of the two units 20a, 20b of FIG. 1),after which the rectified and/ or smoothed output voltages of theseprobes are oppositely connected to the input of the variable-gainamplifier 24 (called second amplifier in connection with the firstembodiment). It has been described before how the amplifier 24influences the automatic adjusting element 302 of the D-C generator 30,for adjusting the electron-beam deflection. The only ditference is thatwith the set-up of FIG. 2, the probes 16a, 16b attain here the nominalvalues of their output voltages with full irradiation (in FIG. 1, thesame probes were irradiated only half by the fannedout beam).

The diap'hragms 18a, 18b are somewhat Wider in FIG. 2 than in the firstembodiment, so as to shield both pairs of probes. Otherwise themechanical structure is identical. As to the electric circuit, thepreviously described units 28, 30 (with 302), 32 and 34 are alsoidentical.

The second embodiment shows a protective circuit 38' which is acted uponby both generators 28, 30 so as to cut off the main supply and/or thehigh voltage applied to the equipment, and particularly to the voltagedivider 34 If both generator outputs should be monitored with theprotective circuit, a multi-grid thyratron may be used in the circuitsshown in FIGS. 1 and 2, each grid receiving the appropriate controlvoltage from a separate network similar to that shown at 384 (FIG. 1).

In the arrangement of FIG. 2, it is readily possible to use, instead ofthe output voltages of the fully irradiated probes 16a, 16b, therectified and/ or smoothed output voltages of the partly irradiatedprobes 46a, 46b, for the formation of the difference in a variable-gainamplifier (like the one described at 22), and thence for the formationof a control or adjusting order for the element 302 of generator 30(circuit not further illustrated). The regulation would then be evenmore sensitive to deviations of 10 the fanned-out electron beam from itsoptimum symmetrical position.

The foregoing disclosure relates only to preferred, exemplaryembodiments of the invention, which is intended to include all changesand modifications of the examples described within the scope of theinvention as set forth in the objects and the appended claims.

We claim:

1. An equipment for controlling and monitoring the electron beam of ahorizontal-type particle accelerator serving for the irradiation ofmaterials, and having a D-C high-voltage source,

a beam generator fed by said D-C source and operatively connected with ahorizontal-type accelerator tube emitting a substantially horizontalelectron beam,

beam guide means,

electromagnet means at the exit end of said beam guide means and havingat least two windings,

one of said windings being excited by a direct current for deflectingsaid electron beam from the substantially horizontal into asubstantially vertical direction,

the other one of said windings being excited by an alternating currentfor fanning out the deflected electron beam, comprising, in combination,

a probe assembly arranged in front of said exit end of the beam guidemeans, between said exit end and said materials,

means for laterally adjusting said probe assembly according toprevailing operating conditions,

first generator means for supplying said direct current for said onewinding,

second generator means for supplying said alternating current for saidother winding,

first adjusting means for said first generator means,

second adjusting means for said second generator means,

means for controlling said first adjusting means by an electricparameter proportional to the acceleration voltage of said particleaccelerator,

means for regulating said first adjusting means in dependence on thevalue of an output voltage derived from said probe assembly, and

means for regulating said second adjusting means in dependence on saidvalue of the output voltage.

2. A controlling and monitoring equipment as defined in claim 1, whereinsaid probe assembly includes two probes which can be set with said probeadjusting means oppositely and symmetrically to a central portion of thedeflected and fanned-out electron beam, cor-responding to the Width ofsaid materials, and which probes are irradiated only partly with saidfanned-out electron beam so as to attain nominal values of their outputvoltages, further comprising first and second variable-gain diflerentialamplifiers for said probes,

rectifier means interposed between said probes and the respectiveamplifiers, and

a reference voltage source providing a constant voltage output, andwherein the outputs of said rectifier means are connected in said firstamplifier so as to form a sum which is oppositely connected to saidconstant voltage output,

the deviation of the diflerence between said sum and said constantvoltage output from a predetermined nominal value is amplified andinfluences said second adjusting means with a view to regulating theamplitude of said alternating current, while said outputs of therectifier means are oppositely connected to one another in said secondamplifier, and

the deviation of the difference between said outputs from apredetermined nominal value is amplified and influences said firstadjusting means with a view to regulating said direct current.

3. A controlling and monitoring equipment as defined 1 1 in claim 2,further comprising a feed-back circuit between the output of said firstgenerator means and the input of said second amplifier, for insuring thestability of operation of said first generator means.

4. A controlling and monitoring equipment as defined in claim 2, whereinsaid outputs of the rectifier means have substantially equal nominalvalues so that said sum corresponds to the level of said constantvoltage output.

5. A controlling and monitoring equipment as defined in claim 1, whereinsaid probe assembly includes an inner and an outer pair of probes whichcan be set with said probe adjusting means oppositely and symmetricallyto a central portion of the deflected and fanned-out electron beam,corresponding to the Width of said materials,

the probes in each pair which are closer to said central beam portionare completely irradiated With said fanned-out electron beam, while theprobes ineach pair which are farther from said central beam portion areirradiated only partly,

so that all probes attain nominal values of their output voltages,further comprising first and second indicating amplifiers for said innerand said outer pairs of probes,

a variable-gain differential amplifier for said inner pair of probes,and

rectifier means interposed between both probes of said inner pair andsaid difierential amplifier, and wherein the outputs of said rectifiermeans are oppositely connected to one another in said differentialamplifier, and

the deviation of the difference between said outputs from apredetermined nominal value is amplified and influences said firstadjusting means with a view to regulating said direct current.

6. A controlling and monitoring equipment as defined in claim 5, furthercomprising visual indicator means actuated by said first and said secondindicating amplifiers, and

manual adjusting means for regulating said second adins-ting means inaccordance with readings taken from said visual indicator means.

7. A controlling and monitoring equipment as defined in claim 5, furthercomprising a feed-back circuit between the output of said firstgenerator means and the input of said difierential amplifier, forinsuring the stability of operation of said first generator means.

8. A controlling and monitoring equipment as defined in claim 5, furthercomprising laterally adjustable grounded metal diaphragms between saidprobe assembly and said material, substantially co-extensivewith theoverall surface of said inner and said outer pairs of probes, forshielding said probe assembly against secondary electrons issuing fromsaid materials. a

9. A controlling and monitoring equipment as defined in claim 1, whereinsaid second generator means includes non-linear circuit elements fordistorting said alternating current so as to constitute a sinusoidalcurrent for said fanning out of said deflected electron beam by way ofsaid other winding of the electromagnet means.

10. A controlling and monitoring equipment as defined in claim 1,further comprising protective circuit means operatively connected withat least one of said generator means for disconnecting said high-voltagesource in case of a disturbance in the respective generator means.

References Cited UNITED STATES PATENTS 3,193,717 7/1965 Nunan 313-76DAVID J. GALVIN, Primary Examiner. JAMES W. LAWRENCE, Examiner. V.LAFRANOHI. Assistant Examiner.

1. AN EQUIPMENT FOR CONTROLLING AND MONITORING THE ELECTRON BEAM OF AHORIZONTAL-TYPE PARTICLE ACCELERATOR SERVING FOR THE IRRADIATION OFMATERIALS, AND HAVING A D-C HIGH-VOLTAGE SOURCE, A BEAM GENERATOR FED BYSAID D-C SOURCE AND OPERATIVELY CONNECTED WITH A HORIZONTAL-TYPEACCELERATOR TUBE EMITTING A SUBSTANTIALLY HORIZONTAL ELECTRON BEAM, BEAMGUIDE MEANS, ELECTROMAGNET MEANS AT THE EXIT END OF SAID BEAM GUIDEMEANS AND HAVING AT LEAST TWO WINDINGS, ONE OF SAID WINDINGS BEINGEXCITED BY A DIRECT CURRENT FOR DEFLECTING SAID ELECTRON BEAM FROM THESUBSTANTIALLY HORIZONTAL INTO A SUBSTANTIALLY VERTICAL DIRECTION, THEOTHER ONE OF SAID WINDINGS BEING EXCITED BY AN ALTERNATING CURRENT FORFANNING OUT THE DEFLECTED ELECTRON BEAM, COMPRISING, IN COMBINATION, APROBE ASSEMBLY ARRANGED IN FRONT OF SAID EXIT END OF THE BEAM GUIDEMEANS, BETWEEN SAID EXIT END AND SAID MATERIALS, MEANS FOR LATERALLYADJUSTING SAID PROBE ASSEMBLY ACCORDING TO PREVAILING OPERATINGCONDITIONS,